Place the sultanas and raisins in a bowl and pour over the hot tea. Cover and allow to soak up the liquid overnight.
Preheat the oven to 170°C/325°F. Line a 2lb loaf tin with baking parchment.
Combine the flour, baking powder, sugar and mixed spice in a mixing bowl. Give it a stir, then mix in the coconut oil and eggs - using a wooden spoon or spatula. Add in the raisins, sultanas and any liquid left in the bowl.
Stir together until everything is thoroughly combined. It will be a very wet dough. Spoon the wet dough into the lined loaf tin, place in the oven and bake for 1 hour - to 1 hour 15 minutes. You'll know it's done when an inserted skewer comes out clean. If you find that the top of the tea bread is starting to look too dark whilst it's in the oven, you can cover it will foil.
Once cooked, remove from the oven and leave to cool in the tin for 10 minutes. Then remove from the tin and allow to cool completely on a wire rack before slicing and serving.
This cake will keep for a week or more wrapped in baking parchment and placed in a sealed container at room temperature (in fact, the cake tastes even better after a day or two).